Doctoral Dissertations

Date of Award

8-1983

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major Professor

H. H. Shugart

Committee Members

D. C. West, S. E. Riechert, P. A. Delcourt, D. E. Reichle

Abstract

The microhabitat utilization and niche characteristics of Peromyscus leucopus, Ochrotomys nuttalli, and Blarina brevicauda were examined within a pine plantation on the Oak Ridge National Environmental Research Park in East Tennessee. Although general microhabitat utilization was the same, niche parameters (such as niche breadth) for each species varied between two study grids, apparently in response to differing understory density. Specialization is thus proposed to be a function of local microhabitat structure. Removal of the generalist species, P. leucopus, from one grid while maintaining the other as a control elicited a significant microhabitat shift and increase in niche breadth by O. nuttalli. B. brevicauda displayed a slight but nonsignificant microhabitat shift and increased niche breadth. These results are a counter example to the hypothesis that generalist species are poor competitors. Spatial micro habitat heterogeneity created by plant secondary succession and extrinsic disturbances such as tree blow-down is suggested to allow coexistence of these species by altering competitive abilities or microhabitat selection at a small spatial scale.

Since interspecific competition affects small mammal niche characteristics, two hypotheses to explain the relative abundances of coexisting animal species are examined. The "niche breadth hypothesis proposes that the more resources controlled by a species the greater will be its abundance. Alternatively, the "habitat availability hypothesis” explains species abundance by the availability of habitat comprising the realized niche. Analysis of the small mammal fauna of the Oak Ridge National Environmental Research Park indicates that habitat availability, not niche breadth, is a good predictor of abundance. This result is discussed in the context of habitat dynamics and the evolutionary history of the species. Results of slug, salamander and bird community analyses also support the habitat availability hypothesis.

Having established the importance of available habitat to animal species abundance, a first-order Markov model is developed to simulate habitat dynamics on landscape islands of differing areal extent. Colonization of these islands is then allowed by animal species having different habitat requirements. The colonization process is modeled using a randomly generated species pool and a species pool adapted to the land scape dynamics regime. Model runs for each species pool were duplicated with the addition of interspecific competition thus totaling four species pool-competition scenarios. Results indicate that the succession/disturbance regime interacts with island area to promote more constant habitat diversity on larger islands. Colonization of the various sized dynamic landscapes resulted in species-area curves having slopes between 0.14 and 0.31, depending on species pool size. Balance between colonization and extinction due to habitat dynamics is the primary cause for this species-area relationship. The model also generates an approximately canonical distribution of species abundances. Patterns of species turnover vary due to species pool composition, competition and vegetation/habitat dynamics on different sized islands.

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